Monday, October 03, 2016

Ultrasonic distance measurement

There are several ways to measure distance without contact. One way is to use ultrasonic waves at 40 kHz for distance measurement. Ultrasonic transducers measure the amount of time taken for a pulse of sound to travel to a particular surface and return as the reflected echo.

The ultrasonic transducers used in rangefinders like the Parallax Ping typically operate at about 40 kHz, but the surplus transducers I purchased have a lower resonant frequency of 24.50khz +/- 0.25khz.

This is the electronic schematic of the homebuilt SONAR. Only one piezoelectric tranducer is used for both tramsmit & receive. This transducer is switched from TX to RX via the four 4016 switches. A high gain amplifier stage & rectifier translates the received echoes into voltage pulses.

This application report describes a distance-measuring system based on ultrasonic sound utilizing the MSP430F413 ultralow-power microcontroller. The system transmits a burst of ultrasonic sound waves towards the subject and then receives the corresponding echo. The MSP430 integrated analog comparator Comparator_A is used to detect the arrival of the echo to the system.

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